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Name______________________
Physical Geography
Lab Activity #07
Due date___________
Rocks & Minerals
COR Objective 8
7.1. Introduction
One part of being a physical geographer is having a basic knowledge of the rocks around
us. In this lab you will get experience handling rock and mineral samples. You will look
for specific characteristics in each sample and by the end of the lab you should have a
good idea as to how rocks form.
7.2. Minerals
Minerals are the building blocks of the rocks and crust around us. Rocks are typically
made up of multiple minerals
1. According to De Blij et al’s Physical Geography, what is the definition of a
mineral?
2. According to De Blij et al’s Physical Geography, what are the most abundant
elements in the Earth’s crust?
In this section of the lab, you will examine some of the mineral samples your instructor
has set out. The ability to describe minerals is straightforward. You will need to identify
the color, luster, crystals, and hardness of each type of mineral.
• Color is rather simple; just look at your sample and describe the color.
• Luster refers to how a mineral reflects light. Is it vitreous (glassy) or dull? Other
luster types include: metallic, adamantine (brilliant like a diamond), resinous,
pearly, and waxy
• Crystals are not present on every mineral sample we have in the lab, but every
mineral has a specific crystalline structure. If you see a crystal on your sample
describe its shape. Is it cubic, hexagonal, etc?
• To test the hardness of a mineral we use the Mohs Scale, developed by the
German mineralogist Frederick Mohs. It ranges from 1-10 with 1 being the
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softest mineral and 10 being the hardest. Below you will see the Mohs ranking of
common objects. For example, your fingernail is a 2.5. If you can scratch a
mineral with your fingernail that means the mineral is less than 2.5. If you cannot
scratch it, it is greater than 2.5.
The Silicates
3. Quartz
Color:
Luster:
Crystals:
Hardness:
4. Feldspar
Color:
Luster:
Crystals:
Hardness:
The Oxides
5. Gypsum
Color:
Luster:
Crystals:
Hardness:
6. Hematite
Color:
Luster:
Crystals:
Hardness:
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The Carbonates
7. Calcite
Color:
Luster:
Crystals:
Hardness:
7.3. Rocks
In this section you will start examining rocks, which are different from minerals.
8. According to De Blij et al’s Physical Geography, what is the definition of a rock?
Rocks fall into three separate classes: Igneous, Sedimentary, and Metamorphic. The
classes refer to how the rock was formed.
• Igneous rocks are those formed from the cooling of molten rock. The way in
which molten rock cools and the minerals inside it determine what rock will form
when it solidifies.
§ Intrusive igneous rocks cool inside the Earth’s crust. Because they cool
under the surface they cool slowly. This slow cooling allows the molten
minerals time to crystallize and gives these rocks a coarse-grained
appearance. Granite is a good example.
§ Extrusive igneous rocks cool outside of the crust. When lava leaves a
volcano it cools quickly, which causes these rocks to be fine-grained.
Basalt is a good example. A rock like obsidian is an example of lava cooling
so quickly that the minerals don’t have time to differentiate leaving a shiny
volcanic glass.
• Sedimentary rocks are those formed from little bits of other rock.
§ Clastic sedimentary rocks form from small pieces of rock being eroded,
deposited, and cemented. Sandstone is simply grains of sand getting glued
into rocks. Shale is finer grained clay cementing together. Often this can
trap deceased creatures and form fossils.
§ Chemically precipitated sedimentary rocks form when the hard parts or
organisms (e.g. shell) or mineral compounds that separate out of water
solutions. Limestone is an example of this. Hydrochloric acid (HCl) can be
used to test for limestone. It reacts with the cemented shell and releases
carbon dioxide while also dissolving the rock. A weaker version of this acid
is found in rainwater and slowly dissolves large amounts of limestone
creating underground caverns.
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• Metamorphic rocks were once igneous or sedimentary rocks that were subjected
to extreme heat and/or pressure. They recrystallize and become totally different
rocks. Limestone turns to marble, sandstone turns to quartzite, and granite turns
to gneiss.
§ Foliation refers to when the minerals of a metamorphic rock align in a
specific direction. Any color or structural pattern you see in the
metamorphic rock samples in the lab can be described as foliation.
Using the rock samples provided by your instructor, study and describe two of each class
of rock. Be thorough and think carefully about what you see in each sample.
Igneous Rocks
Rock Sample 1.
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
Rock Sample 2.
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
Metamorphic Rocks
Rock Sample 3.
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
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Rock Sample 4
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
Sedimentary Rocks
Rock Sample 5
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
Rock Sample 6
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
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7.4. Mystery Rocks
Now you will be tested to see if you have been paying attention. At the back of the lab
you will find three mystery rocks. Using what you have learned in this lab, you should be
able to find the clues in each rock to determine their class and name.
Rock Sample 7.
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
Rock Sample 8.
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
Rock Sample 9.
Color:
Luster:
Structure:
Likely Formation Process:
Rock class and subclass:
Rock name:
End of Lab 7
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